1. Field of the Invention
The present invention relates to a dynamoelectric machine such as an alternator installed on a vehicle, and more particularly, it relates to a structure in which a bearing arranged at each shaft end of a rotor is received in a bearing housing of a bracket.
2. Description of the Related Art
In a known vehicular alternator, a bearing arranged at one end of a shaft of a rotor is received in a bearing housing arranged in a rear bracket, and the rotor is rotatably supported at one shaft end thereof by the rear bracket through the bearing. The bearing is constructed with rolling members being interposed between an outer ring and an inner ring, and the one end of the shaft of the rotor is press-fitted into the inner ring so as to be integrated with the inner ring, and the outer ring is fixedly supported by the bearing housing, whereby the rotor is able to rotate relative to the bearing housing through the bearing. In addition, a plurality of rows of annular grooves are formed on the outer peripheral surface of the outer ring in an axially spaced apart relation with respect to one another with resin bands being fitted into the annular grooves, respectively. Since the resin bands have a coefficient of linear thermal expansion higher than that of the rear bracket (e.g., made of aluminum) and higher than that of the outer ring (e.g., made of iron), the thermal expansion of each resin band due to the generation of heat thereof during operation of the vehicular alternator is greater than the thermal expansion of the bearing housing. As a result, reduction in the coupling or binding force between the bearing housing and the bearing due to a difference in their thermal expansions resulting from the heat generation during operation of the vehicular alternator is suppressed by the thermal expansion of the resin bands, thereby preventing the generation of creep (idling) of the alternator (for instance, see a first patent document: Japanese patent application laid-open No.2002-125346 (particularly FIG. 6 and paragraph Nos. 0029 and 0031).
With the known vehicular alternator, it is necessary to form the annular grooves on the outer peripheral surface of the outer ring so as to arrange therein the resin bands for the purpose of creep prevention. Therefore, the manufacturing cost of the bearing becomes high, giving rise to a problem against the cost reduction of the vehicular alternator.
Moreover, the resin bands are arranged not in the whole range extending axially of the bearing but in a partial area alone, and hence there arises another problem. That is, when an excessive load is applied to the bearing, it is impossible to suppress the generation of creeping of the bearing, so there might be the danger that the bearing housing is subjected to wear and damage.